A series of kinetic and equilibrium measurements of cytochromes c and derivatives thereof will be conducted to investigate the mechanism of the folding of this polypeptide into its native conformation. Kinetic studies will focus on the folding of porphyrin cytochrome c, that is cytochrome c is missing its heme iron, to eliminate the contributions of axial ligation and/or axial ligand exchange suspected in previous kinetic measurements. The viscosity of the folding solvent will be systematically varied to explore the participation of rate limiting diffusion/collision processes in folding. The role of the terminal helices in folding and structural stabilization will be examined by deletion of each helix in turn. Alternatively the effect of covalent attachment of these two helices by a disulfide bond prior to folding will be examined kinetically. Finally, the role of the double covalent attachment of the heme to the polypeptide chain and the charge of the buried porphyrin propionate on the folding mechanism will be examined.